1. Field of the Invention
The present invention relates to an image processing apparatus which reduces color bleeding in a color image.
2. Description of the Related Art
Conventionally, a color which does not originally exist has sometimes appeared as color bleeding at the periphery of a bright portion of a color image due to a chromatic aberration caused by an image pickup optical system. The chromatic aberration caused by the image pickup optical system can be optically reduced to some extent by using a combination of a plurality of lenses including materials with dispersions different from each other. However, recent progress in reduction in size of an image pickup apparatus has required an increase in resolution of a sensor for use in an image pickup element and reduction in size of the image pickup optical system, which makes it difficult to sufficiently suppress the chromatic aberration with a configuration of the image pickup optical system.
The chromatic aberration is broadly classified into a transverse chromatic aberration (a chromatic aberration of magnification) and a longitudinal chromatic aberration (an axial chromatic aberration). The transverse chromatic aberration is a phenomenon in which an imaging position is displaced in a direction along an image plane depending on a wavelength. The longitudinal chromatic aberration is a phenomenon in which the imaging position is displaced in a direction along an optical axis depending on a wavelength. As disclosed in U.S. Pat. No. 6,724,702, the transverse chromatic aberration can be corrected by geometric conversion which adds different distortions to color planes, namely, R (red), G (green), and B (blue). On the other hand, the longitudinal chromatic aberration cannot be corrected by the above-mentioned geometric conversion.
Japanese Patent Laid-Open No. (“JP”) 2007-133592 discloses a method of calculating a correction amount by searching a region in which the G (green) plane is saturated taking advantage of a characteristic that the color bleeding mainly occurs at the periphery of blown-out highlights (a previously-set signal saturation region) and then integrating pixels arranged in regions surrounding the region. JP 2009-268033 discloses a method of determining, as a color-bleeding region, any region in which a pixel value of each color plane in the color image monotonically increases or monotonically decreases and then eliminating such color bleeding.
However, the method disclosed in JP 2007-133592 causes the color bleeding which gives a user a feeling of strangeness also in a region in which the blown-out highlights do not occur, which means that the color bleeding is insufficiently corrected. On the other hand, the method disclosed in JP 2009-268033 can correct the color bleeding also in the region in which the blown-out highlights do not occur. However, since the color bleeding occurs due to the aberration caused by the image pickup optical system, the image pickup optical system which causes an asymmetrical aberration such as coma aberration makes an image of an object have or not have the color bleeding in some directions. When the object has the same type of color as that of the color bleeding, this method is likely to determine the color of the object as the color bleeding in error and thus to eliminate an original color of the object.
Moreover, in order to reduce the color bleeding more effectively, it is necessary to take into consideration the chromatic aberration of magnification caused due to manufacturing variations of the optical system, eccentricity adjustment and, the like.